A nuclear reactor produces electrical power by heating water in a reactor pressure vessel that contains a nuclear fuel core in order to generate steam which is used in turn to drive a steam turbine. The reactor pressure vessel includes a cylinder surrounding the nuclear fuel core. This cylinder is referred to as the core shroud. Feed water is admitted into the reactor pressure vessel and flows through an annular region which is formed between the reactor pressure vessel and the core shroud. Within the annular region, jet pump assemblies are circumferentially distributed around the core shroud.
The core shroud and other components in the reactor pressure vessel are examined periodically to determine their structural integrity and the need for repairs. Visual inspection is a known technique for detecting cracks in nuclear reactor components. The components to be examined may be difficult to access. For example, examination access of the core shroud is limited to the annular space between the outside of the shroud and the inside of the reactor pressure vessel, between adjacent jet pumps.
Further, the inspection areas in a reactor pressure vessel are highly radioactive, and are located under water 50 to 80 feet below the operator's work platform. Thus, inspection of the internal components of the reactor pressure vessel requires a robotic device which can be installed remotely and operated within a narrowly restricted space.
Remote operation is preferred due to safety risks associated with radiation in the reactor. During reactor shutdown, servicing of components typically requires installation of inspection manipulators or devices 30 to 100 feet deep within reactor coolant. The inspection equipment consists of manually controlled poles and ropes to manipulate servicing devices and/or positioning of these devices. Relatively long durations are required to install or remove manipulators and can impact the plant shutdown duration. In addition, different inspection scopes can require several manipulator reconfigurations requiring additional manipulator installations and removals. The long durations cannot only impact plant shutdown durations, but also increase personnel radiation and contamination exposure.
Plant utilities have a desire to reduce the number of manipulator installations and removals to reduce radiological exposure as well as cost and plant outage impact. This invention allows the number of reconfigurations, installations and removals to be minimized. In addition, plant utilities have relatively small working areas near the access point of the reactor cavity. Therefore, the size of the manipulators can impact other activities during plant shutdown.